Siemens and Fjellstrand partner on battery-electric car ferry

11 January 2013

Rendering of the battery-electric car ferry. Click to enlarge.

Siemens, together with the Norwegian shipyard Fjellstrand, has developed a battery-electric car ferry, the miljøferge (environmental ferry) ZeroCat. The 80-meter vessel can carry up to 120 cars and 360 passengers. From 2015 onward, it will serve the E39 route between Lavik and Oppedal, across the Sognefjord. The ship’s batteries will be recharged in the breaks between crossings, a procedure which only takes 10 minutes.

The vessel currently serving this route uses on average one million liters (264 thousand gallons US) of diesel a year and emits 570 metric tons of carbon dioxide and 15 metric tons of nitrogen oxides. The electrically powered ferry was developed for submission to a competition organized by Norway’s Ministry of Transport. As a reward for winning the competition, the shipping company Norled has been granted the license to operate the route until 2025.

The aim of the development section of the competition was to achieve at least 15-20% energy and environmental efficiency in the operation of development ferry. The award criteria for the choice of provider in the final competition was a weighted combination of development ferry’s energy and environmental efficiency (40%) and lowest price on the operation of the ferry route as a whole (60%).

The ferry has been specially designed to accommodate the requirements of an electric drive system. As a catamaran with two slim hulls, it offers less resistance in the water than a conventional vessel. Furthermore, the hulls are made of aluminum instead of steel, which is conventionally used.

Rather than a diesel engine, the ferry is equipped with electric motors to drive the ship’s two screws. These motors are powered by a Li-ion battery weighing 10 metric tons. All in all, the new vessel weighs only half as much as a ferry of conventional design. This saving has a direct impact on the specifications of the drive system.

Whereas the ferry currently serving the route has an engine with an output of 1,500 kW (2,000 hp), the battery in the new vessel will have an output of 800 kW (1,100 hp). In normal conditions, operating at a speed of 10 knots, battery power of 400 kW (536 hp) will suffice.

According to Fjellstrand, the energy required for a crossing of the route at
11 knots is 155 kWh, and at 13 knots, 201 kWh. A full day’s operation would consume 6,300 kWh.

The crucial feature of the new ferry is that it only takes 10 minutes to recharge the 1,000 kWh lithium-polymer battery pack, using a 1,000 kW charger. In the two small villages linked by the ferry, however, the local grid is not equipped to deliver such a large amount of power in such a short space of time. To deal with this problem, batteries have been installed at each port. These serve to recharge the ferry’s battery during turnaround and are then themselves slowly recharged from the local grid.

Hundreds of ferries link Norway’s mainland to the islands off its coast and provide routes across its many fjords. Using today’s battery and recharging technology, all crossings of up to 30 minutes in duration could be served by electrically powered vessels.

The obvious solution to the "can't dock" problem is an EV fleet with V2F (vehicle-to-ferry) integration.

Seriously, the numbers are a bit misleading. 10 minutes at 1 MW may be able to replenish the battery of the 155 kWh used in a typical crossing, but it's not enough for a full recharge of the 1 MWh battery.

Ferry-to-vehicle may be a possibility as well. Cars could be charged using shore power between driving on and the ferry leaving port without depleting the ship's battery. Excess battery power could be dumped to cars during each voyage; the battery depletion could be managed so that it is fully charged during the time at dock.

Usualy port areas have enough power grid capacity and this could reduce project cost. Would be interesting to know whether project is economical and how they expect batteries will survive such frequent cycling.

For this application I do not see any need of reserve generator since battery has 1000 kWh stored energy and using only 155 kWh or only 15%. This would allow more battery cycles.

1) This ferry is radically different, so it is likely WAY more expensive than a normal ferry
- offers less water resistance,
- has hulls made of aluminum,
- weighs only half as much as a conventional ferry.
This means a Diesel powered equivalent would be much less expensive or (if also made expensively light weight) would be very competitive with this abortion in every aspect and superior in most.

2) Hybrid cars do not NOT weigh less than an equivalent ICE model so if this ferry were conventional it might weigh even less then this gold plated monster.

2) Battery costs mean hybrid cars (made in production quantities by the way) are:
- a) a questionable way to save money and
- b) an expensive way to reduce imports and
- c) an expensive way to reduce carbon

- so this monster with triple the number of batteries (a set in the ferry and a set on each end of the route) is an outrageous waste of resources - the "Hummer" of ferries bought by people, with other peoples money, with selfish traits similar to those alleged to Hummer owners.

3) If 12 years and millions of EVs have not pushed battery technology as fast as it can be pushed, THIS will NOT help.

" The award criteria for the choice of provider in the final competition was a weighted combination of development ferry’s energy and environmental efficiency (40%) and lowest price on the operation of the ferry route as a whole (60%)."

Well if the numbers they posted are true, then the new boat uses 77% less energy than the outgoing model. That is a huge reduction.

According to my calculations:
Diesel = 37.6 kWh/gal (LHV)
New boat uses 6,300 kWh/day
per year that is 2,299,500 kWh/yr
Diesel fuel equivalent = 61,157 gal/yr
Compare that to the 264,000 gal/yr of the old boat and you can see that it will save a ton of fuel and be way cheaper to run than the old diesel boat.

What you don't want to do is connect two batteries of different SOC and low internal resistance together, because the surge current between them can cause fireworks. Your DC-DC converter will do the current limiting.

To me a DC-DC converter implies DC-to-AC-to-DC so that transformers, inductors and/or capacitors in the AC section can readily vary the AC output voltage which would, in turn vary the output DC voltage to provide the precise voltage/current desired.

201 kWh in 10 min = ~1.2 MW.

That's a LOT of power to invert into AC and rectify back to DC.

I would think they would instead use some type of ballast or impedance regulator - and/or vary the number of batteries that are in series, to control voltage/current.

If they do, it still might be called a DC-DC converter - I suppose you can call it what you want.

The typical non-isolating DC-DC converter uses an inductor as the energy storage element, switches to source or sink current to the inductor, and blocking and free-wheeling diodes. Here is a page with schematics.

Yes, that is basically the common switching power supply, but we are still talking of switching 1.2 MW, so it might be more practical to dynamically (but slowly) adjust one or both battery stacks (shore stack or ferry stack) to get the voltage match desired.

Continuous fast response would not be needed and the current would only need to be rerouted around one cell for instance, not interrupted.

I know IGBTs and the like have replaced thyristors for HVDC power transmission but long distance power transmission has a big revenue base - I assume they are expensive - maybe not; and maybe cost does not matter.

Instead of switching cells in and out of strings for voltage-balancing (and having to charge-balance them later), electronics do the job with greater reliability anyway. The switches used in HVDC converters handle hundreds of megawatts; the demands of this ferry's charger are small potatoes compared to that, and I suspect that the required hardware is off-the-shelf.

When the 5+ million workers connected to our grid return to their 3+ million electrified homes, on a cold winter day, they create a huge surge in demand (20+ Kw per home with heating, heat pumps, hot water, dryers, kitchen stoves etc) but the grid never fails.

About 3 hours latter, the typical house load drops to less than 4 KW and two or three EVs (per house) could start charging for the next 10 hours or so.

In other words, 5+ million EVs (one per worker) would not overload the current grid when chargers are equipped with proper ($100) timers. Total e-power generation would have to be increased, but that's not a real challenge, there are a lot of Hydro-Wind undeveloped sites.

A (more) steady night load would be very beneficial to our e-power supplier and rates could be reduced from the current $0.065/kWh to about $0.055/kWh. Operating EVs would be very cheap and very clean.